Like all lists of this nature, it is far from definitive. But I have spent enough time hanging around the ole’ internet to know a thing or two. Besides, anyone who browses Firefox extensions for fun has a sickness which is only best channeled through a blog post.

I don’t like a bloated browser so I try to keep customization to a minimum.

All-in-One Sidebar
A useful tool that places bookmarks, history, another web page, and much more in a collapsible sidebar. It also plays well with Sage, if you don’t need a more powerful Feed Reader.
ColorfulTabs
Does what it says and adds a little color to your tabs. I find it helpful for distinguishing the fifteen or so tabs I have open at any given time.
Colt
Adds a “Copy Link + Link Text” to the browser’s context menu.
Delicious Bookmarks
Integrates Del.icio.us Bookmarking with Firefox, my favorite feature is the “Add to Del.icio.us Bookmarks” command to the context menu.
FireFTP
Cleanly integrates an FTP client with Firefox. Fast. Simple. Efficient.
Fireshot
Bar none the best screenshot software for Windows Firefox.
Forecastfox
Simple, unobtrusive weather report.
Hide Menubar
Does what it says. Between hot keys and the All-in-One Sidebar, how often do you use the menu bar anyway?
IE Tab
Use Internet Explorer in Firefox
Menu Editor
A nifty plug-in to organize and simplify context menu (the right-click menu) as well as others.
PDF Download
Allows you to choose between downloading it or viewing it as HTML. Also, don’t be dumb and use Foxit instead of Adobe Reader.
Quicknote
A simple notation tool that integrates well with the All-in-One Sidebar. My favorite feature is the “send to quick note” feature which sends not only the highlighted text but the page link to the notepad.
Session Manager
Remembers your last few firefox sessions, e.g. if you close five tabs, next time it will open the same five.
Sxipper
Saves and manages passwords and textera forms.
Tab Mix Plus
Highly customizable tab behavior. This one is 100% essential.
Twitterfox
One of the many useful Twitter tools, it sits nicely in the lower right hand corner of the browser.